DAANCE Basic Sciences and Anatomy 2 — Questions and Answers
Question 1: The glossopharyngeal nerve (CN IX) provides sensory innervation to the:
- Anterior two-thirds of the tongue
- Posterior one-third of the tongue and pharynx (Correct answer)
- Muscles of mastication
- Parotid gland secretomotor fibers
Correct answer: Posterior one-third of the tongue and pharynx
CN IX carries general and special sensory (taste) fibers from the posterior one-third of the tongue and general sensory fibers from the pharynx.
The anterior two-thirds of the tongue receives general somatic sensation from the lingual nerve (CN V3) and taste from the chorda tympani (CN VII). The posterior third receives all sensation from CN IX. CN IX also carries afferent signals from the carotid body and sinus, relevant to autonomic reflexes during airway manipulation.
Question 2: In the cardiovascular system, the sinoatrial (SA) node functions as:
- The primary pacemaker of the heart (Correct answer)
- A backup pacemaker during SA node failure only
- The site where the QRS complex is generated
- A valve between the atria and ventricles
Correct answer: The primary pacemaker of the heart
The SA node spontaneously depolarizes at 60 to 100 bpm under normal conditions, initiating each heartbeat and serving as the heart primary pacemaker.
Located in the right atrium near the superior vena cava, the SA node generates action potentials that propagate through the atria to the AV node. Increased sympathetic tone accelerates SA node firing; parasympathetic (vagal) tone slows it. Anesthetic agents can alter SA node automaticity.
Question 3: Which respiratory muscle is the primary driver of normal quiet (tidal) breathing?
- External intercostals
- Sternocleidomastoid
- Diaphragm (Correct answer)
- Scalene muscles
Correct answer: Diaphragm
The diaphragm accounts for approximately 70 to 80 percent of tidal volume generation during normal quiet breathing.
During quiet inspiration, diaphragmatic contraction flattens the dome, increasing intrathoracic volume and creating negative pressure that draws air in. Expiration is passive at rest. During sedation, agents that depress the respiratory center or reduce diaphragmatic tone can significantly impair ventilation.
Question 4: The functional residual capacity (FRC) is important in anesthesia because it:
- Represents the maximum volume of air the lungs can hold
- Is the oxygen reserve that delays desaturation during apnea (Correct answer)
- Measures total lung compliance
- Is the volume exhaled during a forced vital capacity maneuver
Correct answer: Is the oxygen reserve that delays desaturation during apnea
FRC is the lung volume at end-expiration and represents the oxygen reservoir available during apnea; lower FRC leads to faster desaturation.
FRC equals ERV plus RV. The oxygen in the alveoli at end-expiration provides a buffer against desaturation. Pre-oxygenation (breathing 100 percent O2 before sedation) increases the FRC oxygen reserve, providing a longer apnea window before critical desaturation.
Question 5: During a Valsalva maneuver, intrathoracic pressure increases, which initially causes:
- An increase in venous return and cardiac output
- A decrease in venous return leading to decreased cardiac output (Correct answer)
- A rise in heart rate from direct sympathetic stimulation
- Immediate hypoxemia from airway closure
Correct answer: A decrease in venous return leading to decreased cardiac output
Elevated intrathoracic pressure compresses the great veins, impeding venous return and reducing preload, transiently decreasing cardiac output.
The Valsalva maneuver (forced expiration against a closed glottis) raises intrathoracic pressure, collapsing the vena cava and reducing preload. Blood pressure drops transiently. The body responds with reflex tachycardia and vasoconstriction.
Question 6: The hepatic first-pass effect refers to:
- Drug absorption through the skin before entering systemic circulation
- Metabolism of orally administered drugs in the liver before reaching systemic circulation (Correct answer)
- The excretion of unchanged drug through the bile
- Drug binding to plasma proteins in the hepatic sinusoids
Correct answer: Metabolism of orally administered drugs in the liver before reaching systemic circulation
After oral absorption, drugs pass through the portal circulation to the liver where they may be extensively metabolized, reducing the amount of active drug reaching systemic circulation.
First-pass metabolism reduces bioavailability of orally administered drugs. For example, oral midazolam has only approximately 35 percent bioavailability due to first-pass metabolism, compared to near 100 percent for IV administration.
DAANCE Basic Sciences and Anatomy 2
The glossopharyngeal nerve (CN IX) provides sensory innervation to the: